Technical Field
[0001] The present invention relates to a bipolar secondary battery in which a seal portion
for preventing leakage of an electrolytic solution from a unit cell has good seal
durability and a production method thereof.
Background Art
[0002] In recent years, hybrid electric vehicles (HEV), electric vehicles (EV) and fuel
cell vehicles have been manufactured and sold and have been continuously developed
from the viewpoint of environmental protection and fuel efficiency improvement. It
is essential to make use of chargeable/dischargeable power sources in these so-called
electric vehicles. As such power sources, secondary batteries e.g. lithium-ion batteries
and nickel-metal-hydride batteries and electric double layer capacitors are used.
In particular, the lithium-ion batteries are suitable for use in the electric vehicles
because of high energy density and high resistance to repeated charge/discharge cycles.
Various developments have been made in the lithium-ion batteries. For use as motor-driving
power sources in the vehicles, it is necessary to connect a plurality of secondary
batteries in series in order to secure high power output.
[0003] When the batteries are connected to each other via connectors, however, the power
output of the batteries becomes decreased due to electrical resistance of the connectors.
Further, the batteries with the connectors are disadvantageous in terms of space efficiency.
That is, the use of the connectors leads to deteriorations in battery output density
and energy density.
[0004] As a solution to these problems, bipolar secondary batteries such as bipolar lithium-ion
secondary batteries have been developed. The bipolar secondary battery has a battery
element that includes a plurality of bipolar electrodes, each of which having a collector,
a positive electrode active material layer formed on one side of the collector and
a negative electrode active material layer formed on the other side of the collector,
laminated together via electrolyte layers and separators. It can also be said that
the positive electrode active material layer, the electrolyte layer and the negative
electrode active material layer constitute one unit cell such that the bipolar secondary
battery has a plurality of unit cells are connected in series via the collectors.
[0005] In the case of using an electrolyte material containing an electrolytic solution,
such as a liquid electrolyte or a polymer gel electrolyte, in the bipolar secondary
battery, there arises a problem that the electrolytic solution leaks from the unit
cell and causes a liquid junction upon contact with the electrolytic solution of the
other unit cell. In order to avoid this problem, Patent Document 1 discloses a bipolar
secondary battery in which seal members formed of a polymeric material such as fluorine
resin rubber, butyl rubber or silicon rubber are arranged around unit cells so as
to seal the unit cells and prevent a liquid junction between the unit cells.
JP 2004185813 discloses a bipolar battery sealed by fusion bonding the outer peripheries of the
collector and the separator.
Prior Art Documents
Patent Documents
[0006] Patent Document 1:
Japanese Laid-Open Patent Publication No. H 09-232003
Summary of the Invention
Problems to be Solved by the Invention
[0007] It is desired that the collectors are formed of a more lightweight material for improvement
in the output density per unit mass of the bipolar secondary battery. Thus, conductive
filler-containing resin materials and conductive polymer materials have been proposed
as collector materials alternative to conventional metal foils.
[0008] In the case of using collectors containing a resin as a base material, it is necessary
to arrange seal members as mentioned above as seal means for sealing the unit cells.
Even though the collector and the seal member are thermally fused together, there
remains an interface between a surface of the collector and a surface of the seal
member. The presence of such an interface between the collector and the seal member
makes it likely that the joint surfaces of the collector and the seal member will
be separated from each other during repeated battery charge/discharge cycles. This
results in a problem that the battery cannot obtain desired seal durability.
Means for Solving the Problems
[0009] The present invention was made in view of the above circumstances. It is accordingly
an object to provide a bipolar secondary battery in which seal means for sealing unit
cells exhibits good seal durability.
[0010] The present inventors have made extensive researches to solve the above problems.
During the process of the researches, the present inventors have changed the conventional
concept that seal members are arrange separately to seal unit cells and come up with
the new idea that seal portions can be formed by bonding collectors together. The
present inventors have then found that it is possible to achieve a remarkably higher
level of seal durability by thermally fusing a pair of opposing collectors to a separator
arranged therebetween than by arranging a conventional seal member. The present invention
is based on such a finding.
[0011] Namely, there is provided according to one aspect of the present invention a bipolar
secondary battery, comprising: a battery element, the battery element comprising:
first and second bipolar electrodes, each of the first and second bipolar electrodes
having a collector disposed with a conductive resin layer, a positive electrode active
material layer formed on one side of the collector and a negative electrode active
material layer formed on the other side of the collector, the conductive resin layer
containing a first resin as a base material; and a separator arranged between the
first and second bipolar electrodes and retaining therein an electrolyte material
to form an electrolyte layer, the separator containing a second resin as a base material;
the positive electrode active material layer of the first bipolar electrode, the electrolyte
layer and the negative electrode active material layer of the second bipolar electrode
constituting a unit cell, wherein a melting point of the first resin is lower than
or equal to a melting point of the second resin; and wherein outer peripheries of
the collectors of the first and second bipolar electrodes and an outer periphery of
the separator are fused together so that the first resin of the outer peripheries
of the collector of the first and second bipolar electrodes is cured in pores of the
separator, to thereby seal an outer peripheral portion of the unit cell.
[0012] There is provided according to another aspect of the present invention a production
method of a bipolar secondary battery, comprising: preparing first and second bipolar
electrodes, each of the first and second electrode having a collector disposed with
a conductive resin layer contains a first resin as base material, a positive electrode
active material layer formed on one side of the collector and a negative electrode
active material layer formed on the other side of the collector; preparing a separator
containing a second resin as a base material; laminating the first and second bipolar
electrodes on the separator in such a manner that the positive electrode active material
layer of the first bipolar electrode faces the negative electrode active material
layer of the second bipolar electrode via the separator; charging an electrolyte material
into the separator to form an electrolyte layer so that the positive electrode active
material layer of the first bipolar electrode, the electrolyte layer and the negative
electrode active material layer of the second bipolar electrode constitute a unit
cell; and hot pressing an outer peripheral portion of the unit cell, thereby fusing
outer peripheries of the collectors of the first and second bipolar electrodes to
an outer periphery of the separator, wherein a melting point of the first resin is
lower than or equal to a melting point of the second resin, wherein in the hot pressing
by the fusing, the first resin of the outer peripheries of the collectors of the first
and second bipolar electrodes is cured in pores of the separator to thereby seal an
outer peripheral portion of the unit cell.
Brief Description of the Drawings
[0013]
FIG. 1 is a schematic section view of a bipolar secondary battery according to one
embodiment of the present invention.
FIG. 2 is a schematic section view of unit cell seal means of the bipolar secondary
battery according to the one embodiment of the present invention.
FIG. 3 is a plan view of a battery assembly according to one embodiment of the present
invention.
FIG. 4 is a front view of the battery assembly according to the one embodiment of
the present invention.
FIG. 5 is a side view of the battery assembly according to the one embodiment of the
present invention.
FIG. 6 is a schematic view of an automotive vehicle having mounted thereon the battery
assembly according to the one embodiment of the present invention.
FIG. 7 is an electron micrograph showing a section of a heat seal portion in a bipolar
secondary battery of Example 1.
DETAILED DESCRIPTION
[0014] Exemplary embodiments of the present invention will be described in detail below
with reference to the drawings. It should be herein noted that the scope of the present
invention is defined based on the claims and is not limited to the following embodiments.
In the drawings, like parts and portions are designated by like reference numerals
to omit repeated explanations thereof. Further, the dimensions of the respective parts
and portions may be exaggerated for purposes of illustration in the drawings and may
be different from the actual dimensions.
[Bipolar Secondary Battery]
[0015] FIG. 1 is a schematic section view showing the overall structure of bipolar secondary
battery 10 according to one embodiment of the present invention. FIG. 2 is an enlarged
section view of part of bipolar secondary battery 10. Bipolar secondary battery 10
has substantially rectangular battery element 21, which actually undergoes a charge/discharge
reaction, sealed in a battery package of laminate film 29.
[0016] Battery element 21 includes a plurality of bipolar electrodes 23 each having collector
11, positive electrode active material layer 13 electrically connected to one side
of collector 11 and negative electrode active material layer 15 electrically connected
to the other side of collector 11 and a plurality of separators 32 each retaining
an electrolyte material in a planar center portion thereof to form electrolyte layer
17. In the present embodiment, collector11 has a conductive resin layer that contains
a first resin as a base material; and separator 32 contains a second resin as a base
material. (The details of these structural parts will be explained later.)
[0017] Bipolar electrodes 23 and separators 32 are alternately laminated on each other in
such a manner that positive electrode active material layer 13 of either one of bipolar
electrodes 23 faces negative electrode active material layer 15 of any other one of
bipolar electrodes 23 adjacent to the aforementioned either one of bipolar electrodes
23 via electrolyte layer 17. Namely, electrolyte layer 17 is arranged between positive
electrode active material layer 13 of the either one of bipolar electrodes 23 and
negative electrode active material layer 15 of the any other one of bipolar electrodes
23 adjacent to the aforementioned either one of bipolar electrodes 23. These adjacently
located positive electrode active material layer 13, electrolyte layer 17 and negative
electrode active material layer 15 constitute one unit cell 19. It can be thus said
that bipolar secondary battery 10 has a laminated structures of unit cells 19. Outermost
collector 11a is located as a positive-electrode-side outermost layer of battery element
21. Positive electrode active material layer 13 is formed only on one side of outermost
collector 11 a. Further, outermost collector 11b is located as a negative-electrode-side
outermost layer of battery element 21. Negative electrode active material layer 15
is formed only on one side of outennost collector 11b. Alternatively, positive electrode
active material layers 13 may be formed on both sides of positive-electrode-side outermost
collector 11a; and negative electrode active material layer 15 may be formed on both
sides of negative-electrode-side outermost collector 11b.
[0018] Bipolar secondary battery 10 also has a positive electrode collector plate 25 located
adjacent to positive-electrode-side outermost collector 11a and led out from laminate
film 29 and a negative electrode collector plate 27 located adjacent to negative-electrode-side
outermost collector 11b and led out from laminate film 29.
[0019] The number of lamination of unit cells 19 is adjusted depending on the desired battery
voltage. It is feasible to decrease the number of lamination of unit cells 19 and
thereby reduce the thickness of bipolar secondary battery 10 as long as bipolar secondary
battery 10 can secure sufficient output. In bipolar secondary battery 10, battery
element 21 is preferably vacuum-sealed in laminate film 29, with some portions of
positive and negative electrode collector plates 25 and 27 led out of laminate film
29, in order to protect battery element 21 from external impact and environmental
deterioration during use.
[0020] In the present embodiment, outer peripheries of collectors 11 of two adjacent bipolar
electrodes 23 are bonded by thermal fusion to an outer periphery of separator 32 so
as to thereby seal outer peripheral portion 31 of unit cell 19 as shown in FIG. 2.
This seal portion has the effect of anchoring collectors 11 to separator 32 as the
first resin contained as the base material in collector 11 melts, flows in and gets
cured within fine pores 33 of separator 32 during thermal fusion. In such thermal
fusion bonding, the molecule of the first resin of collectors 11 is bonded to the
molecule of the second resin of separator 32 by intermolecular force so that there
is no interface formed between the outer periphery of collector 11 and the outer periphery
of separator 32. The strength of bonding between collector 11 and separator 32 can
be thus increased for good seal durability. The formation of such seal mean for unit
cell 19 makes it possible to prevent an electrolytic solution from leaking from unit
cell 19 and causing a short circuit by an electrolytic solution leaking from unit
cell 19 and coming into contact with that of other unit cell 19 and also makes it
possible to prevent contact between adjacent collectors 11 in battery 10 and short
circuit due to slight variations between ends of unit cells 19 in battery element
21. Therefore, the sealing means of the present embodiment provides bipolar secondary
battery 10 with long-term reliability and safety and high quality.
[0021] Although bipolar secondary battery 10 has a substantially rectangular laminated (flat)
battery structure in the present embodiment, the structure of bipolar secondary battery
10 is not particularly limited. Bipolar secondary battery 10 may have any other known
structure such as winding (cylindrical) battery structure. The form of bipolar secondary
battery 10 is not also particularly limited. Bipolar secondary battery 10 can be in
the form of a lithium-ion secondary battery, a sodium-ion secondary battery, a potassium-ion
secondary battery, a nickel-metal-hydride secondary battery, a nickel-cadmium secondary
battery, a nickel-metal-hydride battery or the like. Bipolar secondary battery 10
is preferably a lithium-ion secondary battery in order to increase the voltage of
the electric cell (unit cell 19) and attain high energy density and high output density.
[0022] The main structural parts of bipolar secondary battery 10 will be described in more
detail below.
[Bipolar Electrode]
[0023] Bipolar electrode 23 has collector 11, positive electrode active material layer 13
formed on one side of collector 11 and negative electrode active material layer 15
formed on the other side of collector 11.
(Collector)
[0024] Collector 11 functions as a medium of transferring electrons from one side abutting
positive electrode active material layer 13 to the other side abutting negative electrode
active material layer 15. In the present embodiment, collector 11 has at least one
conductive resin layer and may have any other layer as needed. The conductive resin
layer, which is an essential component of collector 11, functions as electron transfer
medium and contributes to collector weight reduction. This conductive resin layer
contains a first resin as a base material and may contain any other material such
as a conductive filler as needed.
[0025] There is no particular limitation on the first resin used as the base material. Any
known nonconductive polymer material or conductive polymer material can be used as
the first resin without limitation. Suitable examples of the nonconductive polymer
material are polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene
(LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN),
polyimide (PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE),
styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA),
polymethylmethacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF)
and polystyrene (PS). These nonconductive polymer materials show high potential resistance
and solvent resistance. There can also suitably be used thermosetting resins such
as phenol resin, epoxy resin, melamine resin, urea resin and alkyd resin. Suitable
examples of the conductive polymer material are polyaniline, polypyrrole, polythiophene,
polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile and polyoxadiazole.
These conductive polymer materials show sufficient conductivity without the addition
of a conductive filler and thus are advantageous in terms of production process simplification
and collector weight reduction. The above nonconductive and conductive polymer resins
can be used solely or in the form of a mixture of two or more thereof.
[0026] Among others, it is preferable to use a thermoplastic resin for easy fusion bonding
of collectors 11 and separator 32. As the thermoplastic resin can easily melt under
heat, the use of such a thermoplastic resin allows easy sealing of unit cell 19 by
hot pressing etc.
[0027] In order for the resin layer to secure conductivity, a conductive filler is added
to the base material as needed. Especially when the nonconductive polymer material
is used as the first resin, it is necessary to add the conductive filler in order
to impart conductivity to the first resin. There is no particular limitation on the
conductive filler as long as it is a conductive material. A metal material and a conductive
carbon material can be used as the conductive material having good conductivity and
high potential resistance and, in the case where bipolar secondary battery 10 is a
lithium-ion battery, showing lithium-ion shielding properties.
[0028] There is no particular limitation on the metal material. Preferably, the metal material
contains at least one kind of metal selected from the group consisting of Ni, Ti,
Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb and K, or an alloy or oxide thereof. These metal
materials show resistance to positive or negative electrode potential at collector
surface. More preferably, the metal material is an alloy containing at least one kind
of metal selected from the group consisting from Ni, Ti, Al, Cu, Pt, Fe and Cr.
[0029] Specific examples of the alloy are stainless steel (SUS), Inconel (trademark), Hastelloy
(trademark), and other Fe-Cr and Ni-Cr alloys. The use of these alloys makes it possible
that the resin layer can attain higher potential resistance.
[0030] There is also no particular limitation on the conductive carbon material. Preferably,
the conductive carbon material contains at least one kind selected from the group
consisting of acetylene black, Vulcan carbon, Black Pearl, carbon nanofiber, Ketjen
Black, carbon nanotube, carbon nanohorn, carbon nanoballoon and fullerene. These conductive
carbon materials show a very wide potential window so as to be stable to a wide range
of positive and negative potentials and also show good conductivity. The above conductive
fillers such as metal materials and conductive carbon materials can be used solely
or in combination of two or more thereof.
[0031] The form of the conductive filler is not particularly limited and is selected as
appropriate. The conductive filler can in any known form such as particle form, fiber
form, plate form, massive form, cloth form, mesh form etc. In the case of imparting
conductivity to a wide area of the resin, it is preferable to use the conductive filler
in particle form. On the other hand, it is preferable to use the conductive filler
in the form of having a certain directional property e.g. in fiber form in the case
of increasing the conductivity of the resin in a specific direction.
[0032] The size of the conductive filler is not also particularly limited. The conductive
filler can be of various size depending on the size and thickness of the resin layer
and the form of the conductive filler. In the case where the conductive filler is
in particle form, the average particle size of the conductive filler is preferably
of the order of about 0.1 to 10 µm in terms of ease of molding of the resin layer.
In the present specification, the term "particle size" refers to a maximum distance
L between any two points on the contour of a conductive filler particle. The term
"average particle size" refers to an average of the particle sizes of conductive filler
particles observed in several to several ten fields by observation means such as scanning
electron microscope (SEM) or transmission electron microscope (TEM). The same definitions
apply to the particle size and average particle size of the active materials as will
be mentioned later.
[0033] Further, there is no particular limitation on the amount of the conductive filler
added to the resin layer. The conductive filler is not necessarily added to the resin
in the case where the resin contains conductive polymer material and can secure sufficient
conductivity. It is however necessary to add the conductive filler and thereby impart
conductivity to the resin in the case where the resin consists only of nonconductive
polymer material. In this case, the amount of the conductive filler added is preferably
5 to 35 mass%, more preferably 5 to 25 mass%, still more preferably 5 to 15 mass%,
based on the total mass of the nonconductive polymer material. The addition of such
an amount of conductive filler to the resin makes it possible to impart sufficient
conductivity to the nonconductive polymer material while preventing mass increase
in the resin layer.
[0034] There is no particular limitation on the distribution of the conductive filler in
the resin layer. The conductive filler may be uniformly dispersed or partially localized
in the resin base material. In the case of imparting uniform conductivity over the
resin layer, it is preferable to disperse the conductive filler uniformly throughout
the resin. As outer peripheral portion 31 of unit cell 19 is sealed by fusion bonding
of the outer peripheries of collectors 11 and separator 32 in the present embodiment,
it is also effective that the conductive filler is not added to the outer peripheries
of collectors 11 corresponding to such a seal portion but is added to only portions
of collectors 11 on which active material layers 13 and 15 are formed. This makes
it possible to prevent short circuit between collectors 11 in the seal portion and
increase the seal durability of the seal portion to a higher level.
[0035] The thickness of the conductive resin layer alone is preferably 1 to 200 µm, more
preferably 10 to 100 µm, still more preferably 10 to 50 µm. When the thickness of
the resin layer is in the above range, the resistance of the resin layer in a thickness
direction thereof can be limited to a sufficiently low level. This makes it possible
to, in addition to securing the conductivity of collector 11, improve the output density
of battery 10 by weight reduction. This also makes it possible to improve the life
and vibration resistance characteristics of battery 10 by liquid junction reduction.
[0036] There is no particular limitation on the structure of collector 11. Collector 11
can be of any structure as long as the conductive resin layer is contained in collector
11. Collector 11 may have a laminated structure including any other layer as needed
in addition to the resin layer. Examples of the layer other than the resin layer are,
but are not limited to, a metal layer and an adhesive layer. Needless to say, it is
essential that the conductive resin layer is present at a surface of collector 11
in the present embodiment.
[0037] It is desirable that the thickness of collector 11 is smaller for improvement in
battery output density by weight reduction. In bipolar secondary battery 10, the thickness
of collector 11 can be decreased as there would be no problem even when the electrical
resistance of collector 11 between positive and negative electrode active material
layers 13 and 15 in bipolar electrode 23 is high in a direction horizontal to a lamination
direction. In particular, the thickness of collector 11 is preferably 1 to 200 µm,
more preferably 5 to 150 µm, still more preferably 10 to 100 µm. When the thickness
of the collector 11 is in the above range, it is possible that bipolar secondary battery
10 can attain good output characteristics and long-term reliability.
(Positive Electrode Active Material Layer)
[0038] Positive electrode active material layer 13 contains a positive electrode active
material. The positive electrode active material has a composition for absorbing ions
during discharging and releasing ions during charging. In the case where bipolar secondary
battery 10 is a lithium-ion secondary battery, a lithium-transition metal composite
oxide, i.e., a composite oxide of lithium and transition metal can be preferably used
as the positive electrode active material. Specific examples of the lithium-transition
metal composite oxide are: Li-Co composite oxides such as LiCoO
2; Li-Ni composite oxides such as LiNiO
2; Li-Mn composite oxides such as spinel LiMn
2O
4; Li-Fe composite oxides such as LiFeO
2; and those obtained by replacing parts of transition metal elements of the lithium-transition
metal composite oxides with and cycle performance and is available at low cost, the
use of such a lithium-transition metal composite oxide as the positive electrode active
material of bipolar electrode 23 makes it possible that battery 10 can attain good
output characteristics. There can also suitably be used as the positive electrode
active material: lithium-transition metal phosphate or sulfate compounds such as LiFePO
4; transition metal oxides or sulfides such as V
2O
5, MnO
2, TiS
2, MoS
2 and MoO
3; PbO
2; AgO; NiOOH and the like. The above positive electrode active materials can be used
solely or in the form of a mixture of two or more thereof.
[0039] The average particle size of the positive electrode active material is not particularly
limited. In terms of high capacity, reactivity and cycle performance, the average
particle size of the positive electrode active material is preferably 1 to 100 µm,
more preferably 1 to 20 µm. When the average particle size of the positive electrode
active material is in the above range, it is possible to limit increase in the internal
resistance of secondary battery 10 during charging/discharging under high-output conditions
and take out sufficient electric current from secondary battery 10. In the case where
the positive electrode active material is in the form of secondary particles, the
average particle size of primary particles in these secondary particles is preferably
10 nm to 1 µm. The average particle size of the primary particles is not however necessarily
limited to the above range in the present embodiment. Needless to say, the positive
electrode active material is not necessarily in secondary particle form such as aggregate
form or massive form although it depends on the production process. The particle size
of the positive electrode active material and the particle size of the primary particles
can be each given in the unit of a median diameter as measured by laser diffraction.
The form of the positive electrode active material varies depending on the kind and
production process of the positive electrode active material. The positive electrode
active material can be in, but not limited to, spherical (powder) form, plate form,
needle form, columnar form, horn form or the like, and can be used in any form without
problem. It is desirable to select the optimal form of the positive electrode active
material as appropriate for improvement in charging/discharging battery performance.
(Negative Electrode Active Material Layer)
[0040] Negative electrode active material layer 15 contains a negative electrode active
material. The negative electrode active material has a composition for releasing ions
during discharging and absorbing ions during charging. In the case where bipolar secondary
battery 10 is a lithium-ion secondary battery, there is no particular limitation on
the negative electrode active material as long as it is capable of reversibly absorbing
and releasing lithium. Preferable examples of the negative electrode active material
are: metals such as Si and Sn; metal oxides such as TiO, Ti
2O
3, TiO
2, SiO
2, SiO and SnO
2; lithium-transition metal composite oxides such as Li
4/3Ti
5/3O
4 and Li
7MnN; Li-Pb alloy; Li-Al alloy; Li; and carbon materials such as natural graphite,
artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon
and hard carbon. It is preferable that the negative electrode active material contains
an element capable of alloying with lithium so that battery 10 can achieve higher
energy density than those using conventional carbon materials and can attain high
capacity and good output characteristics. The above negative electrode active materials
can be used solely or in the form of a mixture of two or more thereof.
[0041] There is no particular limitation on the element capable of alloying with lithium.
Specific examples of such an element are Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba,
Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te snd Cl. Preferably,
the negative electrode active material contains a carbon material and/or at least
one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In and Zn for
high capacity and energy density of battery 10. It is particularly preferable that
the negative electrode active material contains a carbon material, Si or Sn. These
elements can be used solely or in combination of two or more thereof.
[0042] The average particle size of the negative electrode active material is not particularly
limited. In terms of high capacity, reactivity and cycle performance, the average
particle size of the negative electrode active material is preferably 1 to 100 µm,
more preferably 1 to 20 µm. When the average particle size of the negative electrode
active material is in the above range, it is possible to limit increase in the internal
resistance of secondary battery 10 during charging/discharging under high-output conditions
and take out sufficient electric current from secondary battery 10. In the case where
the negative electrode active material is in the form of secondary particles, the
average particle size of primary particles in these secondary particles is preferably
10 nm to 1 µm. The average particle size of the primary particles is not however necessarily
limited to the above range in the present embodiment. Needless to say, the negative
electrode active material is not necessarily in secondary particle form such as aggregate
form or massive form although it depends on the production process. The particle size
of the negative electrode active material and the particle size of the primary particles
can be each given in the unit of a median diameter as measured by laser diffraction.
The form of the negative electrode active material varies depending on the kind and
production process of the negative electrode active material. The negative electrode
active material can be in, but not limited to, spherical (powder) form, plate form,
needle form, columnar form, horn form or the like, and can be used in any form without
problem. It is desirable to select the optimal form of the negative electrode active
material as appropriate for improvement in charging/discharging battery performance.
[0043] Each of active material layers 13 and 15 may contain any other material such as a
conduction aid, a binder etc. as needed. In the case where an ion conductive polymer
is used, a polymerization initiator may be contained for polymerization of the polymer.
[0044] The conduction aid is an additive to improve the conductivity of active material
layer 13, 15. Examples of the conduction aid are: carbon powders such as acetylene
black, carbon black and Ketjen Black; carbon fibers such as vapor grown carbon fiber
(VGCF; trademark); and expandable graphite. The conduction aid is not however limited
to these materials.
[0045] Examples of the binder are polyvinylidene fluoride (PVdF), polyimide, PTFE, SBR and
synthetic rubber binder. The binder is not however limited to these materials. It
is not necessary to use the binder when the binder is the same material as the matrix
polymer of the gel electrolyte.
[0046] The component ratio of active material layer 13, 15 is not particularly limited and
is adjusted as appropriate in the light of any knowledge about secondary batteries.
The thickness of active material layer 13, 15 is not also particularly limited and
is adjusted in the light of any knowledge about secondary batteries. For example,
the more preferably 20 to 50 µm. When the thickness of active material layer 13, 15
is about 10 µm or more, it is possible to secure sufficient battery capacity. On the
other hand, it is possible to prevent increase in the internal resistance of the battery
due to the difficulty of diffusion of lithium ions to the electrode center (collector
side) when the thickness of active material layer 13, 15 is about 100 µm or less.
[0047] There is no particular limitation of the process of formation of active material
layer 13, 15 on the surface of collector 11. Each of active material layers 13 and
15 can be formed on collector 11 by any known process.
[0048] One example of the active material layer formation process is as follows. First,
an active material slurry is prepared by dispersing and dissolving the active material
and, when needed, the electrolytic salt for improvement in ion conductivity, the conduction
aid for improvement in electronic conductivity, the binder etc. as mentioned above,
into a suitable solvent. The solvent is not particularly limited. There can be used
as the solvent N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetoamide,
methylformamide, cyclohexane, hexane etc. without particular limitation. In the case
of using polyvinylidene fluoride (PVdF) as the binder, NMP can suitably be used as
the solvent. The prepared active material slurry is applied to collector 11, dried
to remove the solvent and pressed, thereby forming active material layer 13, 15 on
collector 11. At this time, the porosity of active material layer 13, 15 can be controlled
by adjusting the press conditions.
[0049] The press means is not particularly limited and is selected as appropriate so as
to control the porosity of active material layer 13, 15 to a desired level. As the
press means, a hot press machine, a calender roll machine and the like are usable.
The press conditions (such as temperature and pressure) are not also particularly
limited and are set as appropriate in the light of any conventional knowledge.
[Electrolyte Layer]
[0050] Electrolyte layer 17 functions as a medium of transferring lithium ions between electrodes.
There is no particular limitation on the electrolyte material of the electrolyte layer
17 as long as the electrolyte material includes an electrolytic solution containing
a solvent. Any known liquid electrolyte or polymer gel electrolyte can be used as
the electrolyte material. In the case where bipolar secondary battery 10 is a lithium-ion
secondary battery, the following liquid electrolyte or polymer gel electrolyte can
preferably be used.
[0051] The liquid electrolyte is one in which a lithium salt as a support salt is dissolved
in a solvent. Examples of the solvent are dimethyl carbonate (DMC), diethyl carbonate
(DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propionate (MP),
methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL),
2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), ethylene
carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and γ-butyrolactone
(GBL). These solvents can be used solely or in the form of a mixture of two or more
thereof.
[0052] The support salt (lithium salt) is not particularly limited. Examples of the support
salt are: inorganic acid anion salts such as LiPF
6, LiBF
4, LiClO
4, LiAsF
6, LiTaF
6, LiSbF
6, LiAlCl
4, Li
2B
10Cl
10, LiI, LiBr, LiCl, LiAlCl, LiHF
2 and LiSCN; and organic acid anion salts such as LiCF
3SO
3, Li(CF
3SO
2)
2N, LiBOB (lithium bis(oxalate)borate) and LiBETI (lithium bis(perfluoroethylene)sulfonylfluoride,
also represented as Li(C
2F
5SO
2)
2N). These electrolytic salts can be used solely or in the form of a mixture of two
or more thereof.
[0053] On the other hand, the polymer gel electrolyte is one in which the above liquid electrolyte
is impregnated into a lithium-ion-conductive matrix polymer. Examples of the lithium-ion-conductive
matrix polymer are: polymer having in a main chain or side chain thereof polyethylene
oxide (PEO); polymer having in a main chain or side chain thereof polypropylene oxide
(PPO); polyethylene glycol (PEG); polyacrylonitrile (PAN); polymethacrylic acid ester;
polyvinylidene fluoride (PVdF); polyvinylidene fluoride-hexafluoropropylene copolymer
(PVdF-HFP); polyacrylonitrile (PAN); poly(methylacrylate) (PMA); and poly(methylmethacrylate)
(PMMA). The above polymers can be used in the form of a mixture, modification, derivative,
random copolymer, alternate copolymer, graft copolymer or block copolymer thereof.
Among others, PEO, PPO, copolymers thereof, PVdF and PVdF-HFP are preferred. In these
matrix polymers, the electrolytic salt such as lithium salt can be dissolved well.
Further, these matrix polymers can provide good mechanical strength by formation of
a cross-linking structure.
[Separator]
[0054] Separator 32 has the function of retaining therein the electrolyte material and contains
a second resin as a base material. In the present embodiment, separator 32 is an essential
component as the seal mean for unit cell 19 is formed by fusion bonding of collectors
11 and separator 32. The second resin contained as the base material in separator
32 needs to be a nonconductive polymer material in order to ensure insulation between
collectors 11. As the second resin, the same nonconductive polymer materials as those
explained above as the first resin contained as the base material in collector 11
can suitably be used without particular limitation.
[0055] There is no particular limitation on the form of separator 32. Separator 32 can be
in the form of a porous membrane (porous film) with a plurality of fine pores, a nonwoven
fabric or a laminate thereof. There can also be used a composite resin membrane that
has a polyolefin nonwoven fabric or polyolefin porous film as a reinforcement layer
and vinylidene fluoride filled in the reinforcement layer.
[0056] In the present embodiment, it is essential that a melting point of the first resin
contained as the base material in collector 11 is lower than or equal to a melting
point of the second resin contained as the base material in separator 32. By satisfaction
of this condition, the first resin contained as the base material in collector 11
melts, flows into fine pores 33 in the surface of separator 32, gets cured within
these fine pores 33 and thereby becomes adhered to the surface of separator 32 during
the thermal fusion bonding of collector 11 and separator 32. It is thus possible to
obtain the anchoring effect for developing remarkable adhesion between collector 11
and separator 32 by embedding a part of the resin of collector 11 into pores 33 of
separator 32. The melting point of the first resin is preferably 20°C or more, more
preferably 50°C or more, lower than the melting point of the second resin.
[0057] Preferable combinations of the first and second resins are as follows. The first
resin preferably contains at least one kind selected from the group consisting of
polyolefins such as polyethylene (melting point: 110 to 130°C) and polypropylene (melting
point: 160 to 170°C). The second resin preferably contains at least one kind selected
from the group consisting of: polyolefins such as polyethylene (melting point: 110
to 130°C) and polypropylene (melting point: 160 to 170°C); polyesters such as polyethylene
terephthalate (melting point: 250 to 260°C) and polyether nitrile (melting point:
269°C); thermoplastic imide (melting point: 380°C); polyamide (melting point: point:
269°C); thermoplastic imide (melting point: 380°C); polyamide (melting point: 176
to 275°C); and polyvinylidene fluoride (melting point: 134 to 169°C). It is possible
to obtain further improvement in seal reliability by selection of the first and second
resins from these resin materials.
[0058] A thermosetting resin that does not melt by heat, such as phenol resin, epoxy resin,
melamine resin, urea resin, alkyd resin and the like is also preferably used as the
second resin as the melting point of the first resin is lower than or equal to the
melting point of the second resin. The use of such a thermosetting resin as the second
resin makes it possible to avoid melting of the second resin during hot pressing etc.
and secure insulation between two collectors 11.
[0059] In the seal means of the present embodiment, the seal portion for sealing unit cell
19 is formed by fusion bonding of collectors 11 and separator 32 without using a seal
member that has been used as conventional seal means. Although the resin of collector
11 melts and flows in pores 33 of separator 32, the viscosity of such a melted resin
is high so that the melted resin is not completely embedded into pores 33 of separator
32. It is possible in the case using e.g. a fine porous film separator as separator
32 to avoid the occurrence of seal leak as the fine porous film separator has through
holes in a vertical direction but does not have a pore passage in a planar direction.
[0060] The conventional seal member plays a role in not only bonding the collectors to each
other and to the separator but also preventing, as an insulation layer, short circuit
between the collectors. As a matter of course, the seal means of the present embodiment
also has the function of preventing short circuit between two collectors 11. The melted
resin of collector 11 is high in viscosity and thus, in general, is not completely
embedded into pores 33 of separator 32 as mentioned above so that there would occur
no short circuit between collectors 11 inside pores 33. It is however conceivable
to adopt the following techniques as a measure to prevent such short circuit more
strictly.
[0061] The first technique for short circuit prevention is to adjust the conditions of the
fusion bonding of collectors 11 and separator 32 as appropriate and, more specifically,
to adjust the temperature, pressure and time of the hot press process in such a manner
that collectors 11 do not come into contact with each other inside pores 33 of and
thereby achieve a desired level of seal durability when only a small amount of the
resin of collector 11 is embedded in pores 33of separator 32. The hot press conditions
depend on the thicknesses of the structural parts and the number of lamination of
the structural parts and cannot be generalized. For example, the hot press conditions
are preferably a pressure of 0.1 to 0.5 Mpa, a temperature of 130 to 180°C and a time
of the order of 3 to 20 seconds in the case of using polyethylene as the base materials
of collector 11 and separator 32.
[0062] The second technique for short circuit prevention is that, in the case of adding
the conductive filler to the conductive resin layer of collector 11, the conductive
filler is not added to the seal portion of the resin layer.
[0063] The third technique for short circuit prevention is to, in the case of adding the
conductive filler to the conductive resin layer of collector 11, control the particle
size of the conductive filler to be larger than the pore size of separator 32. As
the pore size of separator 32 is generally of the order of 100 to 1000 nm, the average
particle size of the conductive filler is preferably controlled to be of the order
of 500 to 5000 nm.
[0064] Although the techniques for short circuit prevention between collectors 11 in the
seal means of the present embodiment has been described above, the measure to prevent
short circuit between collector 11 are not limited to the above techniques and can
be modified, omitted or added as appropriate.
[Battery Package]
[0065] In the present embodiment, laminate film 29 is suitably used as the battery package
because of its high output and cooling characteristics and applicability to large-equipment
batteries such as EV and HEV batteries. Examples of laminate film 29 are aluminum
laminate films such as a three-layer laminate film in which a polypropylene layer,
an aluminum layer and a nylon layer are laminated in this order. Laminate film 29
is formed into e.g. a bag-shaped case so as to cover battery element 21. The form
of laminate film 29 is not however limited to the above. As the battery package, there
can alternatively be used a known metal can.
[Production Method of Bipolar Secondary Battery]
[0066] There is no particular limitation on the production method of bipolar secondary battery
10. For example, bipolar secondary battery 10 can be produced by the following steps:
a step of preparing bipolar electrodes 23 and separators 32 individually; a step of
laminating bipolar electrodes 23 and separators 32 on each other in such a manner
that positive electrode active material layer 13 of one of bipolar electrodes 23 faces
negative electrode active material layer 15 of any other one of bipolar electrodes
23 adjacent to the aforementioned one of bipolar electrodes 23 via separator 32; a
step of charging the electrolyte material in separators 32 to form electrolyte layers
17; and a step of hot pressing the outer peripheral portions of unit cells 19 (battery
element 21) and thereby fusion bonding the outer peripheries of collectors 11 to the
outer peripheries of separators 32. For higher production efficiency, it is herein
feasible to hot press three sides of the outer peripheral portions of the unit cells
19 (battery element 21) to thereby fuse the corresponding areas of the outer peripheries
of collectors 11 and separators 32, charge the electrolyte material in separators
32, and then, hot press the other one side of the outer peripheral portions of unit
cells 19 (battery element 21) to thereby fuse the remaining areas of the outer peripheries
of collectors 11 and separators 32.
[Battery Assembly]
[0067] A battery assembly is manufactured by electrically connecting bipolar secondary batteries
10 in series and/or in parallel in the present embodiment. The capacity and voltage
of the battery assembly is adjusted freely by serial or parallel connection of bipolar
batteries 10.
[0068] FIGS. 3, 4 and 5 are a plan view, a front view and a side view showing the appearance
of one example of battery assembly. As shown in FIGS. 3, 4 and 5, battery assembly
300 has a plurality of attachable/detachable small-size battery modules 250 electrically
connected in series or in parallel. Each of battery modules 250 has a plurality of
bipolar secondary batteries 10 electrically connected in series or in parallel. With
such a configuration, battery assembly 300 can attain high capacity and good output
characteristics suitable for use as a vehicle-driving power source or auxiliary power
source where high volume energy density and high volume output density are required.
Herein, battery modules 250 are electrically connected to each other via electrical
connection means such as busbars and laminated in layers with the use of connection
jig 310. The number of bipolar secondary batteries 10 in battery module 250 and the
number of battery modules 250 in battery assembly 300 are determined depending on
the battery capacity and output characteristics required of a vehicle (electric vehicle)
on which battery assembly 300 is mounted.
[Vehicle]
[0069] Bipolar secondary battery 10 or the battery assembly in which a plurality of bipolar
secondary batteries 10 are combined is suitable for use in a vehicle. In the present
embodiment, bipolar secondary battery 10 has good long-term reliability, good output
characteristics and long life and thus can be mounted on a plug-in hybrid electric
vehicle that features a long EV driving distance or an electric vehicle that features
a long driving distance on a single charge. In other words, bipolar secondary battery
10 or the battery assembly in which a plurality of bipolar secondary batteries 10
are combined can suitably be used as a power source of the vehicle. Examples of the
vehicle are automotive vehicles such as hybrid electric vehicles, electric vehicles
and fuel-cell vehicles. These automotive vehicles refer to not only four-wheel vehicles
(passenger cars, commercial cars e.g. trucks and buses, light cars etc.) but also
two-wheel vehicles (motorbikes etc.) and three-wheel vehicles. The application of
bipolar secondary battery 10 or the battery assembly in which a plurality of bipolar
secondary batteries 10 are combined is not limited to the above automotive vehicles.
Bipolar secondary battery 10 or the battery assembly in which a plurality of bipolar
secondary batteries 10 are combined can be applied as power sources for any other
vehicles e.g. transportation means such as trains and as mountable/installable power
supplies such as uninterruptible power supplies.
[0070] FIG. 6 is a schematic view showing electric vehicle 400 as one example of vehicle
on which battery assembly 300 of FIGS. 3, 4 and 5 is mounted. As shown in FIG. 6,
battery assembly 300 is mounted at a position under a seat in the center of a vehicle
body of electric vehicle 400 so as to secure a wide vehicle interior space and trunk
rooms. The mounting position of battery assembly 300 is not limited to the position
under the seat. Battery assembly 300 may alternatively be mounted in a lower section
of the rear trunk room or an engine room of the vehicle front side. Electric vehicle
400 with battery assembly 300 can attain high durability and ensure sufficient output
during long-term use. The battery assembly can be used for a wide range of applications
such as not only an electric vehicle as shown in FIG. 4 but also a hybrid electric
vehicle and a fuel cell vehicle.
Examples
[0071] The present invention will be described in more detail below by way of the following
examples. It is noted that these examples are only illustrative and not intended to
limit the present invention thereto.
[Production of Bipolar Electrodes]
(Example 1)
[0072] A positive electrode active material paste was prepared by mixing 85 mass% of LiMn
2O
4 as a positive electrode active material, 5 mass% of acetylene black as a conduction
aid, 10 mass% of polyvinylidene fluoride (PVdF) as a binder and an appropriate amount
of N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent. A negative
electrode active material paste was prepared by mixing 85 mass% of Li
4Ti
5O
12 as a negative electrode active material, 5 mass% of acetylene black as a conduction
aid, 10 mass% of polyvinylidene fluoride (PVdF) as a binder and an appropriate amount
of N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent. Further,
a collector was provided in the form of a conductive resin layer (thickness: 30 µm,
volume resistivity in thickness direction: 1 × 10
-2 Ω·cm) containing polyethylene as a base material and carbon particles (average particle
size: 0.8 µm) as a conductive filler. A positive electrode active material layer was
formed on one side of the collector by applying thereto and drying the positive electrode
active material paste. Subsequently, a negative electrode active material layer was
formed on the other side of the collector by applying thereto and drying the negative
electrode active material paste. The thus-obtained laminate of the collector and the
active material layers (hereinafter referred to as "composite electrode material")
was subjected to hot roll pressing at a level that the active material layers did
not break through the collector. The resulting composite electrode material was cut
into a size of 140 × 90 mm, followed by removing the active material layers by a width
of 10 mm around an outer peripheral portion of the composite electrode material. In
this way, there were obtained bipolar electrodes in each of which the positive and
negative electrode active material layers of 120 x 90 mm in size were formed on the
opposite sides of the collector of 140 × 90 mm in size, with the outer periphery of
the collector being exposed by a width of 10 mm as a seal margin.
(Example 2)
[0073] Bipolar electrodes were produced in the same manner as in Example 1, except for using
polypropylene as the base material of the collectors.
(Example 3)
[0074] Bipolar electrodes were produced in the same manner as in Example 1, except for using
polyimide as the base material of the collectors.
(Comparative Example 1)
[0075] Bipolar electrodes were produced in the same manner as in Example 1, except for using
SUS foil films (thickness: 30 µm) as the collectors.
[Production of Bipolar Secondary Battery]
(Examples 1 to 3)
[0076] In each example, a porous film of 150 × 100 mm in size (pore size: 500 nm or smaller)
was placed as a separator on the positive electrode active material layer of one of
the above-obtained bipolar electrodes so as to cover the whole of one side of the
bipolar electrode. The base material of the separator was as indicated in TABLE 1.
Another one of the above-obtained bipolar electrodes was placed on the separator in
such a manner that the negative electrode material layer of the another one bipolar
electrode faced the separator. The above operations were repeated to form a laminate
in which the bipolar electrodes, five in total, were laminated together via the separators.
Three of four peripheral sides of the laminate were subjected to pressing (0.2 MPa,
160°C, 5 seconds) from both top and bottom sides, so as to fuse corresponding areas
of the outer peripheries of the collectors and the separators together. An electrolytic
solution (prepared by dissolving in a mixed solution of propylene carbonate:ethylene
carbonate = 1:1 (volume ratio) LiPF
6 at 1 mol/L) was charged into each of the separators from the remaining one peripheral
side. The thus-obtained laminate was placed under vacuum in a vacuum chamber. In this
state, the remaining one peripheral side of the laminate was subjected to pressing
under the same conditions as above, so as to fuse remaining areas of the outer peripheries
of the collectors and the separators together and thereby vacuum-seal the laminate.
Thus obtained was a battery element in which the outer peripheral portions of the
unit cells were sealed. Two aluminum plates of 130 × 80 mm in size (thickness: 100
µm) having electric lead terminals formed on portions thereof were provided as collector
plates. The battery element was sandwiched between the collector plates and vacuum-sealed
in an aluminum laminate film sheet so as to cover the battery element and the collector
plates by the laminate film sheet. With this, a bipolar battery was completed.
(Comparative Example 1)
[0077] A polyethylene film of 12 mm in width was placed as a seal member on three sides
of a positive-electrode-active-material-layer-side surface of the exposed outer periphery
of the collector of one of the above-obtained bipolar electrodes. A porous film of
150 x 100 mm in size (base material: PE, pore size: 500 nm or smaller) was placed
as a separator on the bipolar electrode and on the seal member. Then, a polyethylene
film of 12 mm in width was placed as a seal member on three peripheral sides of the
separator so as to correspond in position to the previously placed seal member. Another
one of the above-obtained bipolar electrodes was placed in such a manner that the
negative electrode material layer of the another one bipolar electrode faced the separator.
The above operations were repeated to form a laminate in which the bipolar electrodes,
five in total, were laminated together via the separators and the seal members. Three
of four peripheral sides of the laminate were subjected to pressing (0.2 MPa, 160°C,
5 seconds) from both top and bottom sides so as to fuse corresponding areas of the
outer peripheries of the collectors and the separators together by the seal members.
An electrolytic solution (prepared by dissolving in a mixed solution of propylene
carbonate:ethylene carbonate = 1:1 (volume ratio) LiPF
6 at 1 mol/L) was charged into each of the separators from the remaining one peripheral
side. The same seal member as above, two sheets of film per unit cell, was placed
in the remaining one peripheral side of the laminate. The thus-obtained laminate was
placed under vacuum in a vacuum chamber. In this state, the remaining one peripheral
side of the laminate was subjected to pressing under the same conditions as above
so as to fuse remaining areas of the outer peripheries of the collectors and the separators
together and thereby vacuum-seal the laminate. Thus obtained was a battery element
in which the outer peripheral portions of the unit cells were sealed. Two aluminum
plates of 130 × 80 mm in size (thickness: 100 µm) having electric lead terminals formed
on portions thereof were provided as collector plates. The battery element was sandwiched
between the collector plates and vacuum-sealed in an aluminum laminate film sheet
so as to cover the battery element and the collector plates by the laminate film sheet.
between the collector plates and vacuum-sealed in an aluminum laminate film sheet
so as to cover the battery element and the collector plates by the laminate film sheet.
With this, a bipolar battery was completed.
[Charge/Discharge Test]
[0078] Each of the bipolar secondary batteries was subjected to charge/discharge test. The
charge/discharge test was conducted by repeating, in an atmosphere of 60°C, a charge/discharge
cycle of charging the battery to 13.5 V in a constant-current system (CC, current:
1C), leaving the battery at rest for 10 minutes, discharging the battery to 7.5 V
in a constant-current system (CC, current: 1C) and leaving the battery at rest for
10 minutes. The seal durability of the seal portion of the unit cell was then evaluated.
The evaluation results were are indicated below in TABLE 1.
TABLE 1
|
Seal means |
Seal durability |
Collector base material |
Separator base material |
|
Example 1 |
PE |
PE |
Thermal fusion bonding of collectors and separator |
No solution leakage even after 1000 cycles |
Example 2 |
PP |
PP |
No solution leakage even after 1000 cycles |
Example 3 |
PI |
PI |
No solution leakage even after 1000 cycles |
Comparative Example 1 |
Thermal fusion bonding of collectors (PE) and separator (PE) via seal member (PE) |
Solution leakage after 500 cycles |
PE: Polyethylene
PP: Polypropylene
PI: Polyimide |
[0079] The bipolar secondary battery of Comparative Example 1 had a significant drop in
voltage and became incapable of charge/discharge cycle operation at a point exceeding
500 test cycles. It was found as a result of examination of the battery inside that
there occurred leakage of the electrolytic solution from the unit cell due to insufficient
bonding of the seal portion in the battery. On the other hand, each of the bipolar
secondary batteries of Examples 1 to 3 was able to maintain its voltage, with no leakage
of the electrolytic solution observed in the seal portion, even after
1000 test cycles.
[Microscopic Analysis]
[0080] The thermally fused portion (seal portion) of each of the bipolar secondary batteries
of Examples 1-3 was observed by an electron microscope. By way of example, FIG. 7
shows an electron micrograph of the cross section of the thermally fused portion of
the bipolar secondary battery of Example 1. As shown in FIG. 7, the resin base material
of the collector was embedded into the pores of the porous film separator so that
the resin molecule of the collector and the resin molecule of the separator were bonded
and cured together. There was no interface formed between the collector and the separator
in the thermally fused portion of the bipolar secondary battery. In Examples 2 and
3, the resin base material of the collector was also embedded into and cured within
the pores of the porous film separator in the same manner as in Example 1.
[0081] It has been confirmed by the above results that it is possible according to the present
invention to provide the bipolar secondary battery in which the seal means for the
unit cell exhibits good seal durability under by the effect of anchoring the collector
base resin to the separator.
1. A bipolar secondary battery, comprising: a battery element, the battery element comprising:
first and second bipolar electrodes, each of the first and second bipolar electrodes
having a collector disposed with a conductive resin layer, a positive electrode active
material layer formed on one side of the collector and a negative electrode active
material layer formed on the other side of the collector, the conductive resin layer
containing a first resin as a base material; and
a separator arranged between the first and second bipolar electrodes and retaining
therein an electrolyte material to form an electrolyte layer, the separator containing
a second resin as a base material;
the positive electrode active material layer of the first bipolar electrode, the electrolyte
layer and the negative electrode active material layer of the second bipolar electrode
constituting a unit cell,
wherein a melting point of the first resin is lower than or equal to a melting point
of the second resin; and
wherein outer peripheries of the collectors of the first and second bipolar electrodes
and an outer periphery of the separator are fused together, so that the first resin
of the outer peripheries of the collector of the first and second bipolar electrodes
is cured in pores of the separator to thereby seal an outer peripheral portion of
the unit cell.
2. The bipolar secondary battery according to claim 1, wherein the first resin contains
either polyethylene or polypropylene; and wherein the second resin contains at least
one kind selected from the group consisting of polyethylene, polypropylene, polyethylene
terephthalate, polyether nitrile, polyimide, polyamide and polyvinylidene fluoride.
3. The bipolar secondary battery according to claim 1 or 2, wherein the second resin
is a thermosetting resin.
4. The bipolar secondary battery according to any one of claims 1 to 3, wherein the conductive
resin layer contains a conductive filler; and wherein a particle size of the conductive
filler is larger than a pore size of the separator.
5. The bipolar secondary battery according to any one of claims 1 to 4, wherein the bipolar
secondary battery is a lithium-ion secondary battery.
6. The bipolar secondary battery according to any one of claims 1 to 5,
wherein the first resin of the outer peripheries of the collectors of the first and
second bipolar electrodes and the second resin of the outer periphery of the separator
are bonded together by intermolecular force.
7. The bipolar secondary battery, according to any of claims 1 to 6,
wherein a melting point of the first resin is 20°C, or more, lower than a melting
point of the second resin.
8. A production method of a bipolar secondary battery, comprising:
preparing first and second bipolar electrodes, each of the first and second electrode
having a collector disposed with a conductive resin layer containing a first resin
as a base material, a positive electrode active material layer formed on one side
of the collector and a negative electrode active material layer formed on the other
side of the collector;
preparing a separator containing a second resin as a base material;
laminating the first and second bipolar electrodes on the separator in such a manner
that the positive electrode active material layer of the first bipolar electrode faces
the negative electrode active material layer of the second bipolar electrode via the
separator;
charging an electrolyte material into the separator to form an electrolyte layer so
that the positive electrode active material layer of the first bipolar electrode,
the electrolyte layer and the negative electrode active material layer of the second
bipolar electrode constitute a unit cell; and
hot pressing an outer peripheral portion of the unit cell, thereby fusing outer peripheries
of the collectors of the first and second bipolar electrodes to an outer periphery
of the separator,
wherein a melting point of the first resin is lower than or equal to a melting point
of the second resin; and
wherein, in the hot pressing, by the fusing, the first resin of the outer peripheries
of the collector of the first and second bipolar electrodes is cured in pores of the
separator to thereby seal an outer peripheral portion of the unit cell.
9. The production method of the bipolar secondary battery according to claim 8, wherein
the hot pressing includes hot pressing all sides other than one side of the outer
peripheral portion of the unit cell so as to fuse corresponding areas of the outer
peripheries of the collectors of the first and second bipolar electrodes and of the
separator together.
10. The production method of the bipolar secondary battery according to claim 9, wherein
the hot pressing includes, after charging the electrolyte material into the separator,
hot pressing the one side of the outer peripheral portion of the unit cell so as to
fuse remaining areas of the outer peripheries of the collectors of the first and second
bipolar electrodes and of the separator together.
1. Bipolare Sekundärbatterie, umfassend: ein Batterieelement, wobei das Batterieelement
umfasst:
erste und zweite bipolare Elektroden, wobei jede der ersten und zweiten bipolaren
Elektroden einen Kollektor besitzt, der mit einer leitfähigen Harzschicht ausgestattet
(disposed) ist, eine Positivelektrodenaktivmaterialschicht, die auf einer Seite des
Kollektors gebildet ist, und eine Negativelektrodenaktivmaterialschicht, die auf der
anderen Seite des Kollektors gebildet ist, wobei die leitfähige Harzschicht ein erstes
Harz als ein Basismaterial enthält; und
einen Separator, der zwischen den ersten und zweiten bipolaren Elektroden angeordnet
ist, und der ein Elektrolytmaterial aufnimmt, um eine Elektrolytschicht zu bilden,
wobei der Separator ein zweites Harz als ein Basismaterial enthält;
wobei die Positivelektrodenaktivmaterialschicht der ersten bipolaren Elektrode, die
Elektrolytschicht und die Negativelektrodenaktivmaterialschicht der zweiten bipolaren
Elektrode eine Einheitszelle ausbilden,
wobei der Schmelzpunkt des ersten Harzes niedriger oder gleich ist zu einem Schmelzpunkt
des zweiten Harzes; und
wobei äußere Peripherien der Kollektoren der ersten und zweiten bipolaren Elektroden
und eine äußere Peripherie des Separators zusammengeschmolzen sind, so dass das erste
Harz der äußeren Peripherien des Kollektors und der ersten und zweiten bipolaren Elektroden
in Poren des Separators gehärtet ist, wodurch ein äußerer peripherer Anteil der Einheitszelle
abgedichtet wird.
2. Die bipolare Sekundärbatterie gemäß Anspruch 1, wobei das erste Harz entweder Polyethylen
oder Polypropylen enthält; und wobei das zweite Harz mindestens eine Art enthält,
ausgewählt aus der Gruppe, bestehend aus Polyethylen, Polypropylen, Polyethylenterephthalat,
Polyethernitril, Polyimid, Polyamid und Polyvinylidenfluorid.
3. Die bipolare Sekundärbatterie gemäß Anspruch 1 oder 2, wobei das zweite Harz ein heißhärtendes
Harz ist.
4. Die bipolare Sekundärbatterie gemäß einem der Ansprüche 1 bis 3, wobei die leitfähige
Harzschicht einen leitfähigen Füllstoff enthält; und wobei eine Partikelgröße des
leitfähigen Füllstoffs größer ist als eine Porengröße des Separators.
5. Die bipolare Sekundärbatterie gemäß einem der Ansprüche 1 bis 4, wobei die bipolare
Sekundärbatterie eine Lithiumionensekundärbatterie ist.
6. Die bipolare Sekundärbatterie gemäß einem der Ansprüche 1 bis 5, wobei das erste Harz
der äußeren Peripherien des Kollektors und der ersten und zweiten bipolaren Elektroden
und das zweite Harz der äußeren Peripherie des Separators aneinander durch intermolekulare
Kraft gebunden sind.
7. Die bipolare Sekundärbatterie gemäß einem der Ansprüche 1 bis 6,
wobei ein Schmelzpunkt des ersten Harzes 20°C, oder mehr, geringer ist als ein Schmelzpunkt
des zweiten Harzes.
8. Herstellungsverfahren einer bipolaren sekundären Batterie, umfassend:
Herstellen von ersten oder zweiten bipolaren Elektroden, wobei jeder der ersten und
zweiten Elektrode einen Kollektor besitzt, der mit einer leitfähigen Harzschicht ausgestattet
(disposed) ist, die ein erstes Harz als ein Basismaterial enthält, einer Positivelektrodenaktivmaterialschicht,
die an einer Seite des Kollektors gebildet wird, und einer Negativelektrodenaktivmaterialschicht,
die an der anderen Seite des Kollektors gebildet wird;
Herstellen eines Separators, der ein zweites Harz als ein Basismaterial enthält; und
Laminieren der ersten und zweiten bipolaren Elektroden auf den Separator in solch
einer Weise, dass die Positivelektrodenaktivmaterialschicht der ersten bipolaren Elektrode
in Richtung der Negativelektrodenaktivmaterialschicht der zweiten bipolaren Elektrode
mittels des Separators ausgerichtet ist;
Füllen eines Elektrolytmaterials in den Separator, um eine Elektrolytschicht zu bilden,
so dass die Positivelektrodenaktivmaterialschicht der ersten bipolaren Elektrode,
die Elektrolytschicht und die Negativelektrodenaktivmaterialschicht der zweiten bipolaren
Elektrode eine Einheitszelle ausbilden; und
Heißpressen eines äußeren peripheren Anteils der Einheitszelle, wobei äußere Peripherien
des Kollektors der ersten und zweiten bipolaren Elektroden an eine äußere Peripherie
des Separators geschmolzen werden,
wobei ein Schmelzpunkt des ersten Harzes niedriger oder gleich ist zu einem Schmelzpunkt
des zweiten Harzes; und
wobei, während des Heißpressens, durch das Schmelzen, das erste Harz der äußeren Peripherien
des Kollektors der ersten und zweiten bipolaren Elektroden in Poren des Separators
gehärtet wird, wodurch ein äußerer peripherer Anteil der Einheitszelle abgedichtet
wird.
9. Das Herstellungsverfahren der bipolaren sekundären Batterie gemäß Anspruch 8, wobei
das Heißpressen das Heißpressen aller Seiten, außer einer Seite des äußeren peripheren
Anteils der Einheitszelle, beinhaltet, so dass entsprechende Flächen der äußeren Peripherien
der Kollektoren der ersten und zweiten bipolaren Elektroden und des Separators zusammengeschmolzen
werden.
10. Das Herstellungsverfahren der bipolaren sekundären Batterie gemäß Anspruch 9, wobei
das Heißpressen, nach dem Füllen des Elektrolytmaterials in den Separator, das Heißpressen
von einer Seite des äußeren peripheren Anteils der Einheitszelle beinhaltet, so dass
verbleibende Flächen der äußeren Peripherien der Kollektoren der ersten und zweiten
bipolaren Elektroden und des Separators zusammengeschmolzen werden.
1. Batterie secondaire bipolaire comprenant : un élément de batterie, l'élément de batterie
comprenant :
des première et seconde électrodes bipolaires, chacune des première et seconde électrodes
bipolaires possédant un collecteur comportant une couche de résine conductrice, une
couche de matériau actif d'électrode positive formée sur un côté du collecteur, et
une couche de matériau actif d'électrode négative formée sur l'autre côté du collecteur,
la couche de résine conductrice contenant une première résine comme matériau de base,
et
un dispositif de séparation agencé entre les première et seconde électrodes bipolaires
et contenant un matériau d'électrolyte afin de former une couche d'électrolyte, le
séparateur contenant une seconde résine en tant que matériau de base,
la couche de matériau actif d'électrode positive de la première électrode bipolaire,
la couche d'électrolyte et la couche de matériau actif d'électrode négative de la
seconde électrode bipolaire constituant une cellule élémentaire,
dans laquelle le point de fusion de la première résine est inférieur ou égal au point
de fusion de la seconde résine, et
dans laquelle les zones périphériques externes des collecteurs des première et seconde
électrodes bipolaires et la périphérie externe du séparateur sont fondues ensemble
de telles sortes que la première résine des zones périphériques externes du collecteur
des première et seconde électrodes bipolaires est durcie en pores du séparateur pour
rendre ainsi étanche la partie périphérique de la cellule élémentaire.
2. Batterie secondaire bipolaire selon la revendication 1, dans laquelle la première
résine contient soit du polyéthylène, soit du polypropylène, et dans laquelle la seconde
résine contient au moins un type de constituant sélectionné à partir du groupe constitué
de polyéthylène, polypropylène, polyéthylène téréphtalate, polyéther nitrile, polyimide,
polyamide et polyfluorure de vinylidène.
3. Batterie secondaire bipolaire selon la revendication 1 ou 2, dans laquelle la seconde
résine est une résine thermodurcissable.
4. Batterie secondaire bipolaire selon l'une quelconque des revendications 1 à 3, dans
laquelle la couche de résine conductrice contient une charge conductrice, et dans
laquelle la taille des particules de la charge conductrice est supérieure à la taille
des pores du dispositif de séparation.
5. Batterie secondaire bipolaire selon l'une quelconque des revendications 1 à 4, dans
laquelle la batterie secondaire bipolaire est une batterie secondaire lithium - ion.
6. Batterie secondaire bipolaire selon l'une quelconque des revendications 1 à 5,
dans laquelle la première résine des zones périphériques externes des collecteurs
des première et seconde électrodes bipolaires et la seconde résine de la périphérie
externe du séparateur sont soudées ensemble par une force intermoléculaire.
7. Batterie secondaire bipolaire selon l'une quelconque des revendications 1 à 6,
dans laquelle le point de fusion de la première résine est 20 °C ou plus, inférieur
au point de fusion de la seconde résine.
8. Procédé de fabrication d'une batterie secondaire bipolaire, comprenant :
la préparation de première et seconde électrodes bipolaire, chacune des première et
seconde électrodes possédant un collecteur comportant une couche de résine conductrice
qui contient une première résine en tant que matériau de base, une couche de matériau
actif d'électrode positive formée sur un côté du collecteur et une couche de matériau
actif d'électrode négative formée sur l'autre côté du collecteur,
la préparation d'un dispositif de séparation contenant une seconde résine comme matériau
de base,
la stratification des première et seconde électrodes sur le séparateur de manière
à ce que la couche de matériau actif d'électrode positive de la première électrode
bipolaire se trouve en face de la couche de matériau actif d'électrode négative de
la seconde électrode bipolaire par l'intermédiaire du séparateur,
le chargement du matériau d'électrolyte dans le séparateur pour former une couche
d'électrolyte de telle sorte que la couche de matériau actif d'électrode positive
de la première électrode bipolaire, la couche d'électrolyte et la couche de matériau
actif d'électrode négative de la seconde électrode bipolaire constituent une cellule
élémentaire, et
le pressage à chaud de la partie périphérique externe de la cellule élémentaire, ce
qui fait ainsi fondre les zones périphériques externes des collecteurs des première
et seconde électrodes sur la périphérie externe du séparateur,
dans lequel le point de fusion de la première résine est inférieur ou égal au point
de fusion de la seconde résine, et
dans lequel, dans le pressage à chaud, grâce à la fusion, la première résine des zones
périphériques externes du collecteur des première et seconde électrodes est durcie
en pores du séparateur pour rendre ainsi étanche la partie périphérique externe de
la cellule élémentaire.
9. Procédé de fabrication de la batterie secondaire bipolaire selon la revendication
8, dans lequel le pressage à chaud inclut un pressage à chaud de tous les côtés différents
du premier côté de la partie périphérique externe de la cellule élémentaire de façon
à faire fondre ensemble des zones correspondantes appartenant aux zones périphériques
externes des collecteurs des première et seconde électrodes et du séparateur.
10. Procédé de fabrication de la batterie secondaire bipolaire selon la revendication
9, dans lequel le pressage à chaud inclut, après avoir chargé le matériau d'électrolyte
dans le séparateur, un pressage à chaud du premier côté de la partie périphérique
externe de la cellule élémentaire de façon à faire fondre ensemble les zones restantes
appartenant aux zones périphériques externes des collecteurs des première et seconde
électrodes et du séparateur.